This invention relates to an air control valve for use in a vehicle emissions control system.
Modern automobiles are equipped with catalytic converters to control emissions. In order to meet increasingly stringent governmental requirements, it is necessary to inject air supplied from an engine operated air pump to the engine exhaust stream. The air supply must be supplied to different points in the exhaust stream, depending upon the vehicle operating conditions. For example, when the vehicle engine is warm, the air supply is injected downstream into the exhaust manifold, but when the vehicle engine is cold, the air supply is normally injected upstream closer to the combustion chamber. However, even during cold engine operation, the air supply must be momentarily diverted from the upstream injection point to the downstream injection point when the vehicle is decelerated. After a time period of a few seconds, the injection returns to the upstream injection point regardless of whether or not the vehicle is still decelerating. In order to accomplish the relatively complicated diverting functions required, prior art air control valves were relatively complicated, and, accordingly, were rather bulky, expensive, and heavy. Furthermore, these prior art valves required two vacuum signal connections between the valve and engine manifold vacuum.
The present invention provides a unique two piston actuated valve, which requires only a signal vacuum connection. The actuating piston is connected directly to the valve element. The auxiliary piston is shifted in response to the vacuum communication to the valve, and remains in the shifted position as long as the vacuum signal remains. The actuator piston is provided with a check valve, which permits uninhibited communication across the piston in one direction, and restricted communication in the other direction. Accordingly, when the vacuum signal increases to a predetermined amount more than that required to actuate the valve, the actuator piston will deflect, thereby actuating the valve element, for a few seconds until the pressure is equalized across the actuator piston, and thereafter will return to a position communicating the air supply to the upstream injection point.